Load control device for a light-emitting diode light source

ABSTRACT

A load control device for controlling power delivered from a power source to an electrical load may comprise a control circuit configured to control the load regulation circuit to control the power delivered to the electrical load. The control circuit may be configured to operate in an AC mode when an input voltage is an AC voltage and in a DC mode when the input voltage is a DC voltage. The control circuit may be configured to disable the power converter in the DC mode. The control circuit may be configured to render a controllable switching circuit conductive in the AC mode, and non-conductive in the DC mode. The rectifier circuit may be configured to rectify the input voltage to generate a rectified voltage when the input voltage is an AC voltage, and to pass through the input voltage when the input voltage is a DC voltage.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/327,198, filed Apr. 25, 2016, all of which is incorporated byreference in its entirety.

BACKGROUND

Light-emitting diode (LED) light sources (such as, for example, LEDlight engines) are often used in place of or as replacements forconventional incandescent, fluorescent, or halogen lamps, and the like.LED light sources may comprise a plurality of light-emitting diodesmounted on a single structure in a suitable housing. LED light sourcesare typically more efficient and provide longer operational service ascompared to incandescent, fluorescent, and halogen lamps. In order toilluminate properly, an LED driver is typically coupled between analternating-current (AC) source and the LED light source for regulatingthe power supplied to the LED light source. The LED driver may regulateeither the voltage provided to the LED light source to a particularvalue, the current supplied to the LED light source to a specific peakcurrent value, or both the current and the voltage. Examples of LEDdrivers are described in greater detail in commonly-assigned U.S. Pat.No. 8,492,987, issued Jul. 23, 2010, and U.S. Pat. No. 8,680,787, issuedMar. 25, 2014, both entitled LOAD CONTROL DEVICE FOR A LIGHT-EMITTINGDIODE LIGHT SOURCE, the entire disclosures of which are herebyincorporated by reference.

As the electrical infrastructure changes to accommodate renewable energysources (e.g., wind power, photovoltaic solar power, full cells, etc.),it is likely that there will be a movement towards DC power distributionas this is the native version of generation for many of thesetechnologies. For example, photovoltaic solar arrays generate DC powerand often this is directly stored in batteries. From there, power may beprovided directly from the batteries, or it may be inverted toalternating current for use by appliances. With this anticipated move toa DC power bank, it would be desirable to provide power directly as DCpower rather than convert it to AC power. Many AC electrical loadsactually use DC power to perform their functions, and traditionallyrequire rectification, and often, active power factor correction (PFC),to make the AC power useful to the electrical load. However, therectification and active power factor correction operations introduce anefficiency loss.

SUMMARY

As described herein, a load control device for controlling powerdelivered from a power source to an electrical load may comprise a powerconverter configured to generate a bus voltage across a bus capacitor; aload regulation circuit configured to receive the bus voltage and tocontrol the power delivered to the electrical load; and a controlcircuit configured to control the load regulation circuit to control thepower delivered to the electrical load. The control circuit may beconfigured to operate in an AC mode when an input voltage is an ACvoltage, and in a DC mode when the input voltage is a DC voltage. Thecontrol circuit may be configured to disable the power converter in theDC mode, for example, when the power required by the load is less than athreshold amount. In addition, the control circuit may be configured tocontrol the power converter circuit to adjust the magnitude of the busvoltage towards a target bus voltage, and adjust the target bus voltageas a function of the power required by the load, when the power requiredby the load is greater than the threshold amount in the DC mode.Additionally, or alternatively, the control circuit may be configured toreduce the target bus voltage in the DC mode.

The load control device may comprise a controllable switching circuitelectrically coupled in series with the bus capacitor. The controlcircuit may be configured to render the controllable switching circuitconductive in the AC mode and non-conductive in the DC mode. The controlcircuit may include a rectifier circuit that includes input terminalsand a DC detect circuit. The rectifier circuit may also include aplurality (e.g., two) controllable switching circuits. The DC detectcircuit may be electrically coupled between the input terminals of therectifier circuit. The DC detect circuit may be configured to render thecontrollable switching circuits of the rectifier circuit conductive whenthe voltage across the DC detect circuit is a DC voltage (e.g., andrender them non-conductive when the voltage across the DC detect circuitis AC voltage). The load control device may also include a ripple detectcircuit (e.g., AC ripple detect circuit) that is configured to receive arectified voltage and generate a ripple detect signal that indicateswhether AC ripple is present in the rectified voltage. The ripple detectcircuit may provide the ripple detect signal to the control circuit, andthe control circuit may be configured to determine whether the inputvoltage is AC voltage or DC voltage based on the ripple detect signal.

The rectifier circuit may be configured to rectify the input voltage togenerate a rectified voltage when the input voltage is an AC voltage,and to pass through the input voltage when the input voltage is a DCvoltage. The rectifier circuit may comprise: (1) first and second inputterminals (e.g., AC input terminals); (2) first and second outputterminals (e.g., DC output terminals); (3) a first diode configured toconduct current from the first input terminal to the first outputterminal; (4) a second diode configured to conduct current from thesecond output terminal to the second input terminal; (5) a third diodeconfigured to conduct current from the second input terminal to thefirst output terminal; (6) a fourth diode configured to conduct currentfrom the second output terminal to the first input terminal; (7) a firstcontrollable switching circuit (e.g., a MOSFET) coupled in parallel withthe first diode; and (8) a second controllable switching circuit (e.g.,a MOSFET) coupled in parallel with the second diode. The first andsecond switching circuits may be rendered non-conductive when a voltageacross the input terminals is an AC voltage and rendered conductive whenthe voltage across the input terminals is a DC voltage. The rectifiercircuit may also comprise a DC detect circuit that may be electricallycoupled between the input terminals and may be configured to render thefirst and second controllable switching circuits conductive when thevoltage across the DC detect circuit is a DC voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of an example light-emitting diode(LED) driver for controlling the intensity of an LED light source.

FIG. 2 is an example plot of a target bus voltage as a function of anamount of power required by an electrical load.

FIG. 3 is an example diagram of an AC ripple detect circuit for an LEDdriver.

FIG. 4 is a simplified schematic diagram of an example isolated,half-bridge forward converter and a current sense circuit of an LEDdriver.

FIG. 5 is a simplified schematic diagram of an example rectifiercircuit.

FIG. 6 are example waveforms illustrating the operation of the rectifiercircuit of FIG. 5.

FIG. 7 is an example diagram of a DC detect circuit for an LED driver.

FIG. 8 is a simplified flowchart of an example control procedureexecuted by a control circuit of a load control device (e.g., an LEDdriver).

DETAILED DESCRIPTION

FIG. 1 is a simplified block diagram of a load control device, e.g., alight-emitting diode (LED) driver 100, for controlling the amount ofpower delivered to an electrical load, such as an LED light source 102(e.g., an LED light engine), and thus the intensity of the electricalload. The LED light source 102 is shown as a plurality of LEDs connectedin series, but may comprise a single LED, or a plurality of LEDsconnected in parallel, or a suitable combination thereof, depending onthe particular lighting system. The LED light source 102 may compriseone or more organic light-emitting diodes (OLEDs). The LED driver 100may comprise a first input terminal 104 (e.g., a hot terminal) and asecond input terminal 106 (e.g., a neutral terminal) that are adapted tobe coupled to a power source (not shown), such as, e.g., analternating-current (AC) power source, or a direct-current (DC) powersource. The first and second input terminals 104, 106 may be configuredto receive an input voltage V_(IN), e.g., an AC mains input voltage, ora DC input voltage.

The LED driver 100 may comprise a radio-frequency (RFI) filter circuit110, a rectifier circuit 120, a boost converter 130, a load regulationcircuit 140, a control circuit 150, a current sense circuit 160, amemory 170, a communication circuit 172, and/or a power supply 180. TheRFI filter circuit 110 may minimize the noise provided on the AC mains.The rectifier circuit 120 may be a dynamic rectifier circuit configuredto change its operation in response to whether an AC voltage or a DCvoltage is present at the input terminals 104, 106 (as will be describedin greater detail below with reference to FIGS. 4 and 5). The rectifiercircuit 120 may be configured to rectify the input voltage V_(IN) togenerate a rectified voltage V_(RECT) when the input terminals areconnected to an AC power source and an AC voltage is present at theinput terminals 104, 106. The rectifier circuit 120 may be configured topass through the input voltage V_(IN) (e.g., not rectify the inputvoltage V_(IN)) when the input terminals are connected to a DC powersource and a DC voltage is present at the input terminals 104, 106.

The boost converter 130 may receive the rectified voltage V_(RECT) andgenerate a boosted direct-current (DC) bus voltage V_(BUS) across a buscapacitor C_(BUS) (such as, e.g., an electrolytic capacitor). The boostconverter 130 may comprise any suitable power converter circuit forgenerating an appropriate bus voltage, such as, for example, a flybackconverter, a single-ended primary-inductor converter (SEPIC), a Ćukconverter, or other suitable power converter circuit. The boostconverter 130 may operate as a power factor correction (PFC) circuit toadjust the power factor of the LED driver 100 towards a power factor ofone. The LED driver 100 may comprise an input capacitor C_(IN) (such as,e.g., a film capacitor) coupled across the input of the boost converter130. Examples of LED drivers having boost converters are described ingreater detail in commonly-assigned U.S. Pat. No. 8,492,987, issued Jul.23, 2013, and U.S. Pat. No. 8,680,787, issued Mar. 25, 2014, bothentitled LOAD CONTROL DEVICE FOR A LIGHT-EMITTING DIODE LIGHT SOURCE,the entire disclosures of which are hereby incorporated by reference.

The load regulation circuit 140 may receive the bus voltage V_(BUS) andcontrol the amount of power delivered to the LED light source 102, forexample, to control the intensity of the LED light source 102 between alow-end (i.e., minimum) intensity L_(LE) (e.g., approximately 1-5%) anda high-end (i.e., maximum) intensity L_(HE) (e.g., approximately 100%).An example of the load regulation circuit 140 may be an isolated,half-bridge forward converter. An example of the load control device(e.g., LED driver 100) comprising a forward converter is described ingreater detail in commonly-assigned U.S. Pat. No. 9,253,829, issued Feb.2, 2015, entitled LOAD CONTROL DEVICE FOR A LIGHT-EMITTING DIODE LIGHTSOURCE, the entire disclosure of which is hereby incorporated byreference. The load regulation circuit 140 may comprise, for example, abuck converter, a linear regulator, or any suitable LED drive circuitfor adjusting the intensity of the LED light source 102.

The control circuit 150 may be configured to control the operation ofthe boost converter 130 and/or the load regulation circuit 140. Thecontrol circuit 150 may comprise, for example, a digital controller orany other suitable processing device, such as, for example, amicrocontroller, a programmable logic device (PLD), a microprocessor, anapplication specific integrated circuit (ASIC), or a field-programmablegate array (FPGA). The control circuit 150 may generate a bus voltagecontrol signal V_(BUS-CNTL), which may be provided to the boostconverter 130 for adjusting the magnitude of the bus voltage V_(BUS)towards a target bus voltage V_(BUS-TARGET). The control circuit 150 mayreceive a bus voltage feedback control signal V_(BUS-FB) from the boostconverter 130, which may indicate the magnitude of the bus voltageV_(BUS).

The control circuit 150 may generate drive control signals V_(DR1),V_(DR2). The drive control signals V_(DR1), V_(DR2) may be provided tothe load regulation circuit 140 for adjusting the magnitude of a loadvoltage V_(LOAD) generated across the LED light source 102, and/or themagnitude of a load current LOAD conducted through the LED light source120, for example, to control the intensity of the LED light source 120to a target intensity L_(TRGT). The control circuit 150 may adjust anoperating frequency fop and/or a duty cycle DC_(INV) (e.g., an on-timeT_(ON) as a percentage of the period T) of the drive control signalsV_(DR1), V_(DR2) to adjust the magnitude of the load voltage V_(LOAD)and/or the load current I_(LOAD). The control circuit 150 may receive aload voltage feedback signal V_(V-LOAD) generated by the load regulationcircuit 140. The load voltage feedback signal V_(V-LOAD) may indicatethe magnitude of the load voltage V_(LOAD).

The current sense circuit 160 may receive a sense voltage V_(SENSE)generated by the load regulation circuit 140. The sense voltageV_(SENSE) may indicate the magnitude of the load current I_(LOAD). Thecurrent sense circuit 160 may receive a signal-chopper control signalV_(CHOP) from the control circuit 150. The current sense circuit 160 maygenerate a load current feedback signal V_(I-LOAD), which may be a DCvoltage indicating the average magnitude I_(AVE) of the load currentI_(LOAD). The control circuit 150 may receive the load current feedbacksignal V_(I-LOAD) from the current sense circuit 160 and control thedrive control signals V_(DR1), V_(DR2) accordingly. For example, thecontrol circuit 150 may control the drive control signals V_(DR1),V_(DR2) to adjust a magnitude of the load current I_(LOAD) to a targetload current I_(TRGT) to thus control the intensity of the LED lightsource 102 to the target intensity L_(TRGT) (e.g., using a controlloop). The control circuit 150 may be configured to determine a loadpower P_(LOAD) presently being consumed by the LED light source 102using the load voltage feedback signal V_(V-LOAD) and the load currentfeedback signal V_(I-LOAD). The load current I_(LOAD) may be the currentthat is conducted through the LED light source 120. The target loadcurrent I_(TRGT) may be the desired current that the control circuit 150would ideally cause to be conducted through the LED light source 120(e.g., based at least on the load current feedback signal V_(I-LOAD)).

The control circuit 150 may be coupled to the memory 170. The memory 170may store operational characteristics of the LED driver 100 (such as,e.g., the target intensity L_(TRGT), the low-end intensity L_(LE), thehigh-end intensity L_(HE), etc.). The communication circuit 172 may becoupled to, for example, a wired communication link, or a wirelesscommunication link, such as a radio-frequency (RF) communication link oran infrared (IR) communication link. The control circuit 150 may beconfigured to update the target intensity L_(TRGT) of the LED lightsource 102 and/or the operational characteristics stored in the memory170 in response to digital messages received via the communicationcircuit 172. The LED driver 100 may be operable to receive aphase-control signal from a dimmer switch for determining the targetintensity L_(TRGT) for the LED light source 102. The power supply 180may receive the rectified voltage V_(RECT) and generate a direct-current(DC) supply voltage V_(CC) for powering the circuitry of the LED driver100.

The LED driver 100 may also comprise a ripple detect circuit 190, whichmay receive the rectified voltage V_(RECT) and may generate a rippledetect signal V_(RIP-DET) that may indicate whether AC ripple is presentin the rectified voltage V_(RECT) (i.e., whether an AC voltage iscoupled to the input terminals 104, 106). The control circuit 150 mayreceive the ripple detect signal V_(RIP-DET), and may operate in an ACmode if an AC voltage is coupled to the input terminals 104, 106, or aDC mode if a DC voltage is coupled to the input terminals. The rippledetect circuit 190 may also be coupled to receive the input voltageV_(IN) and/or the bus voltage V_(BUS). The LED driver 100 may alsocomprise a controllable switching circuit 192 (e.g., including a MOSFET)electrically coupled in series with the bus capacitor C_(BUS) fordisconnecting the bus capacitor, as will be described in greater detailbelow.

When operating in the AC mode, the control circuit 150 may enable theoperation of the boost converter 130 to generate the bus voltage V_(BUS)across the bus capacitor C_(BUS). The control circuit 150 may render thecontrollable switching circuit 192 conductive and may control themagnitude of the bus voltage V_(BUS) to a maximum magnitude V_(BUS-MAX)(e.g., approximately 465 volts). The control circuit 150 may alsooperate the boost converter 130 as a PFC circuit during the AC mode toadjust the power factor of the LED driver 100 towards a power factor ofone.

When operating in the DC mode, the control circuit 150 may be configuredto disable the operation of the boost converter 130 to reduce power lossin the LED driver 100, for example, due to the power loss in the boostconverter when enabled. When disabled, the boost converter 130 may passthrough the DC voltage from the input terminals 104, 106, and the busvoltage V_(BUS) may have a minimum magnitude V_(BUS-MIN) (e.g.,approximately 380 volts). When operating in the DC mode, the controlcircuit 150 may be configured to enable the boost converter 130 during astartup routine of the LED driver 100, and disable the boost converterduring normal operation.

The control circuit 150 may render the controllable switching circuit192 non-conductive to disconnect the bus capacitor C_(BUS) in the DCmode because the bus capacitor C_(BUS) may not be required when a DCvoltage is present at the input terminals 104, 106. The LED driver 100may also comprise a capacitor C_(FILM) (e.g., a film capacitor) coupledacross the input of the load regulation circuit 140 for supplyinghigh-frequency current that may be required to circulate through theload regulation circuit. Because the bus capacitor C_(BUS) may compriseone or more electrolytic capacitors, disconnecting the bus capacitorC_(BUS) may increase the lifetime of the LED driver 100. In addition,disconnecting the bus capacitor C_(BUS) may reduce an inrush currentconducted by the LED driver 100 when power is first applied to the inputterminals 104, 106.

The control circuit 150 may also enable the operation of the boostconverter 130 in the DC mode when the power P_(LOAD) required by LEDlight source 102 exceeds a threshold amount P_(TH) (e.g., approximately80%). In addition, the control circuit 150 may also be configured tocontrol the target bus voltage V_(BUS-TARGET) as a function of the powerP_(LOAD) required by LED light source 102, for example, as shown in FIG.2. The control circuit 150 may be configured to adjust the target busvoltage V_(BUS-TARGET) linearly between the minimum magnitudeV_(BUS-MIN) and the maximum magnitude V_(BUS-MAX) when the powerP_(LOAD) required by LED light source 102 is above the threshold amountP_(TH). The control circuit 150 may be configured to control the targetbus voltage V_(BUS-TARGET) using open loop control, for example, byusing a lookup table to determine the target bus voltage V_(BUS-TARGET)in response to the target intensity L_(TRGT) and/or target load currentI_(TRGT). The control circuit 150 may also be configured to control thetarget bus voltage V_(BUS-TARGET) using closed loop control, forexample, by using the load voltage feedback signal V_(V-LOAD) and theload current feedback signal V_(I-LOAD) to determine the power P_(LOAD)required by LED light source 102. The control circuit 150 may beconfigured to learn the target intensity L_(TRGT) and/or the target loadcurrent I_(TRGT) at which the power P_(LOAD) required by LED lightsource 102 exceeds the threshold amount P_(TH) (e.g., during a startuproutine).

The control circuit 150 may be configured to temporarily increase themagnitude of the bus voltage V_(BUS) during transient events (e.g., whenincreasing and/or decreasing the target intensity L_(TRGT) and/or thetarget load current I_(TRGT)).

Rather than disabling the boost converter 130 in the DC mode, thecontrol circuit 150 may also scale back the operation of the boostconverter (e.g., reduce the target bus voltage V_(BUS-TARGET)) so as toreduce losses in the boost converter.

FIG. 3 is an example diagram of an AC ripple detect circuit 300 for anLED driver. The AC ripple detect circuit 300 may be an example of the ACripple detect circuit 190 of the LED driver 100 shown in FIG. 1. The ACripple detect circuit 300 may include resistors R310, R312, capacitorC314, and diodes D316, D318. The AC ripple detect circuit 300 mayreceive the rectified voltage V_(RECT) and may generate the rippledetect signal V_(RIP-DET). The control circuit 150 may receive theripple detect signal V_(RIP-DET) and may determine whether AC voltage orDC voltage is connected to the input terminals (e.g., the inputterminals 104, 106). For example, the control circuit 150 may receivethe ripple detect signal V_(RIP-DET) and determine whether AC ripple ispresent in the rectified voltage V_(RECT).

If AC voltage is present at the input terminals 104, 106, a full-waverectified voltage may be present at the resistor R310. The full-waverectified voltage may be twice the normal line frequency. The full-waverectified voltage may be divided via the resistors R310, R312, and thedivided voltage may charge the capacitor C314 and be fed through thediode D318 to generate the ripple detect signal V_(RIP-DET). If DCvoltage is present at the input terminals 104, 106, the voltage presentat the resistor R310 will not be characterized by a significant ACfrequency component. As such, the capacitor C314 will not charge,resulting in the ripple detect signal V_(RIP-DET) having a lower value(e.g., 0 volts) than instances where AC voltage is present at the inputterminals 104, 106. Accordingly, the control circuit 150 may receive theripple detect signal V_(RIP-DET), and may operate in an AC mode if an ACvoltage is coupled to the input terminals 104, 106, or a DC mode if a DCvoltage is coupled to the input terminals. The ripple detect circuit 300may also be coupled to receive the input voltage V_(IN) and/or the busvoltage V_(BUS).

FIG. 4 is a simplified schematic diagram of an isolated, half-bridgeforward converter 440 and a current sense circuit 460 of an LED driver(e.g., the LED driver 100 shown in FIG. 1). The forward converter 440may be an example of the load regulation circuit 140 of the LED driver100 shown in FIG. 1. The current sense circuit 460 may be an example ofthe current sense circuit 160 of the LED driver 100 shown in FIG. 1.

The forward converter 440 may comprise a half-bridge inverter circuithaving two field effect transistors (FETs) Q410, Q412 for generating ahigh-frequency inverter voltage V_(INV) from the bus voltage V_(BUS).The FETs Q410, Q412 may be rendered conductive and non-conductive inresponse to the drive control signals V_(DR1), V_(DR2). The drivecontrol signals V_(DR1), V_(DR2) may be received from the controlcircuit 150. The drive control signals V_(DR1), V_(DR2) may be coupledto the gates of the respective FETs Q410, Q412 via a gate drive circuit414 (e.g., which may comprise part number L6382DTR, manufactured by STMicroelectronics). The control circuit 150 may generate the invertervoltage V_(INV) at a constant operating frequency fop (e.g.,approximately 60-65 kHz) and thus a constant operating period T_(OP).However, the operating frequency fop may be adjusted under certainoperating conditions. For example, the operating frequency fop may bedecreased near the high-end intensity L_(HE). The control circuit 150may be configured to adjust a duty cycle DC_(INV) of the invertervoltage V_(INV) to control the intensity of an LED light source 402towards the target intensity L_(TRGT). The control circuit 150 mayadjust the duty cycle DC_(INV) of the inverter voltage V_(INV) to adjustthe magnitude (e.g., the average magnitude I_(AVE)) of the load currentI_(LOAD) towards the target load current I_(TRGT). The magnitude of theload current I_(LOAD) may vary between a maximum rated current I_(MAX)and a minimum rated current I_(MIN).

The inverter voltage V_(INV) may be coupled to the primary winding of atransformer 420 through a DC-blocking capacitor C416 (e.g., which mayhave a capacitance of approximately 0.047 μg), such that a primaryvoltage V_(PRI) is generated across the primary winding. The transformer420 may be characterized by a turns ratio n_(TURNS) (i.e., N₁/N₂), whichmay be approximately 115:29. A sense voltage V_(SENSE) may be generatedacross a sense resistor R422, which may be coupled in series with theprimary winding of the transformer 420. The secondary winding of thetransformer 420 may generate a secondary voltage that may be coupled tothe input terminals of a full-wave diode rectifier bridge 424 forrectifying the secondary voltage generated across the secondary winding.The positive output terminal of the rectifier bridge 424 may be coupledto the LED light source 402 through an output energy-storage inductorL426 (e.g., which may have an inductance of approximately 10 mH), suchthat the load voltage V_(LOAD) may be generated across an outputcapacitor C428 (e.g., which may have a capacitance of approximately 3μF).

The current sense circuit 460 may comprise an averaging circuit forproducing the load current feedback signal V_(I-LOAD). The averagingcircuit may comprise a low-pass filter comprising a capacitor C430(e.g., which may have a capacitance of approximately 0.066 uF) and aresistor R432 (e.g., which may have a resistance of approximately 3.32kΩ). The low-pass filter may receive the sense voltage V_(SENSE) via aresistor R434 (e.g., which may have a resistance of approximately 1 kΩ).The current sense circuit 460 may comprise a transistor Q436 (e.g., aFET as shown in FIG. 4) coupled between the junction of the resistorsR432, R434 and circuit common. The gate of the transistor Q436 may becoupled to circuit common through a resistor R438 (e.g., which may havea resistance of approximately 22 kΩ). The gate of the transistor Q436may receive the signal-chopper control signal V_(CHOP) from the controlcircuit 150. An example of the current sense circuit 460 may bedescribed in greater detail in commonly-assigned U.S. Pat. No.9,232,574, issued Jan. 5, 2016, entitled FORWARD CONVERTER HAVING APRIMARY-SIDE CURRENT SENSE CIRCUIT, the entire disclosure of which ishereby incorporated by reference.

FIG. 5 is a simplified schematic diagram of an example rectifier circuit500 (e.g., the rectifier circuit 120 of the LED driver 100 shown in FIG.1). The rectifier circuit 500 may comprise first and second inputterminals 502, 504 (e.g., AC input terminals) and first and secondoutput terminals 506, 508 (e.g., DC output terminals). The rectifiercircuit 500 may comprise a full-wave rectifier including four diodes510, 512, 514, 516. The first diode 510 may be electrically coupledbetween the first input terminal 502 and the first output terminal 506,and may be configured to conduct current from the first input terminal502 to the first output terminal 506. The second diode 512 may beelectrically coupled between the second input terminal 504 and thesecond output terminal 508, and may be configured to conduct currentfrom the second output terminal 508 to the second input terminal 504.The third diode 514 may be electrically coupled between the second inputterminal 504 and the first output terminal 506, and may be configured toconduct current from the second input terminal 504 to the first outputterminal 506. The fourth diode 516 may be electrically coupled betweenthe first input terminal 502 and the second output terminal 508, and maybe configured to conduct current from the second output terminal 508 tothe first input terminal 502.

The rectifier circuit 500 may comprise a first controllable switchingcircuit 520 (e.g., a MOSFET) having main terminals electrically coupledin parallel with the first diode 510, and a second controllableswitching circuit 522 (e.g., a MOSFET) having main terminalselectrically coupled in parallel with the second diode 512. The firstand second diodes 510, 512 may be body diodes of the first and secondcontrollable switching circuits 520, 522, respectively, or may beimplemented as separate parts. The rectifier circuit 500 may beconfigured to operate in an AC mode when a voltage (e.g., an inputvoltage) across the input terminals 502, 504 is an AC voltage, and in aDC mode when the voltage across the input terminals is a DC voltage. Thefirst and second switching circuits 520, 522 may be renderednon-conductive in the AC mode (e.g., when the voltage across the inputterminals is an AC voltage), and rendered conductive in the DC mode(e.g., when the voltage across the input terminals is a DC voltage).

The rectifier circuit 500 may further comprise a rectifier controlcircuit, such as a DC detect circuit 530, coupled between the inputterminals 502, 504 to receive the voltage across the input terminals.The DC detect circuit 530 may be configured to generate gate drivevoltages V_(G1), V_(G2) that may be coupled to gate terminals of theMOSFETs of the first and second controllable switching circuits 520,522, respectively, for rendering the first and second controllableswitching circuits conductive and non-conductive.

FIG. 6 illustrates example waveforms of the rectifier circuit 500 whenthe rectifier circuit is operating in the AC mode and in the DC mode.The DC detect circuit 530 may be configured to control the magnitudes ofthe first and second gate drive voltages V_(G1), V_(G2) towards acircuit common (e.g., approximately zero volts) to render the first andsecond controllable switching circuits 520, 522 non-conductive in the ACmode when the input voltage (e.g., the voltage across the inputterminals 502, 504) is an AC voltage. The DC detect circuit 530 may beconfigured to control the magnitudes of the first and second gate drivevoltages V_(G1), V_(G2) towards a supply voltage V_(CC) (e.g., asgenerated by the power supply 180 of the LED driver 100 in FIG. 1) torender the first and second controllable switching circuits 520, 522conductive in the DC mode when the input voltage (e.g., the voltageacross the terminals 502, 504) is a DC voltage.

FIG. 7 is an example diagram of a DC detect circuit 700 for an LEDdriver. The DC detect circuit 700 may be an example of the DC detectcircuit 530 of FIG. 5. As such, the DC detect circuit 700 may be part ofa rectifier circuit, such as the rectifier circuit 500 shown in FIG. 5.The DC detect circuit 700 may include two input terminals, such as thefirst and second input terminals 502, 504 (e.g., AC input terminals) ofthe rectifier circuit 500. Further, the DC detect circuit may beconnected to two output terminals through an AC/DC rectifier circuit,such as the first and second output terminals 506, 508 (e.g., DC outputterminals) of the rectifier circuit 500. Accordingly, the DC detectcircuit 700 may be configured to generate gate drive voltages forcontrolling controllable switching circuits, such as the gate drivevoltages V₁, V_(G2) that are coupled to gate terminals of the MOSFETs ofthe first and second controllable switching circuits 520, 522,respectively, for rendering the first and second controllable switchingcircuits conductive and non-conductive. In this regard, the DC detectcircuit may operate whether it is coupled to an AC voltage or to a DCvoltage via the input terminals 502, 504.

The DC detect circuit 700 may include capacitors C702, C720, and C722,resistors R704, R714, R718, R726, and R730, Zener diodes Z706, Z708, andZ716, a diode D724, a MOSFET 710, and an NPN transistor 728. The DCdetect circuit 700 may include a power supply, or use a power supply ofthe LED drive, such as the power supply 180, for example.

When an AC voltage is coupled to the input terminals 502, 504, thecombination of the capacitor C702 and resistor R704 will cause there tobe a net zero DC voltage across the capacitor C702. As a result, theMOSFET 520 will be non-conductive and in diode mode across diode 510.Further, when an AC voltage is coupled to the input terminals 502, 504,the combination of the capacitor C722 and resistor R726 will cause thereto be a net zero DC voltage across the capacitor C722. For example, theNPN transistor 728 may see pulsing currents at its gate, rendering theNPN transistor 728 conductive and causing the capacitor C720 todischarge. The discharge of the capacitor C720 may cause the MOSFET 522to be rendered non-conductive and in diode mode across the diode 512.Accordingly, when an AC voltage is coupled to the input terminals 502,504, the DC detect circuit will not drive either of the MOSFETs 520, 522to be conductive such that the diodes 510, 512, 514, 516 act as afull-wave rectifier.

When a DC voltage is coupled to the input terminals 502, 504, the Zenerdiodes Z706, Z708 will clamp the input DC voltage and cause thecapacitor C702 to charge. When the capacitor C702 is charged, the MOSFET710 will turn on, which will drive the first gate drive voltage V_(G1)towards a supply voltage V_(CC) (e.g., as generated by the power supply180 of the LED driver 100 in FIG. 1) and render the MOSFET 520conductive. Further, when a DC voltage is coupled to the input terminals502, 504, the capacitor C722 will charge and there will not be pulsingcurrents flowing through R726 (e.g., as is seen when AC voltage iscoupled to the input terminals). As a result, the NPN transistor 728will be rendered non-conductive, which will drive the second gate drivevoltage V_(G2) towards the supply voltage V_(CC) and render the MOSFET522 conductive. When the MOSFETs 520, 522 are conductive, the voltagelosses across the diodes 510, 512 are eliminated.

FIG. 8 is a simplified flowchart of an example control procedure 800that may be executed by a control circuit of a load control device(e.g., the control circuit 150 of the LED driver 100). For example, thecontrol procedure 800 may be executed periodically to control the LEDdriver to operate in an AC mode or a DC mode in response to rippledetected on an input voltage of the LED driver. At 802, the controlcircuit may determine whether the ripple detect signal V_(RIP-DET)indicates that AC voltage or DC voltage is coupled to the inputterminals (e.g., the input terminals 104, 106). If the control circuitdetermines that AC voltage is coupled to the input terminals at 802,then the control circuit may operate in AC mode at 804. For example, thecontrol circuit may ensure that the bus capacitor is connected at 806.For instance, the control circuit may connect the bus capacitor byclosing a switch (e.g., the controllable switching circuit 192) at 806.The control circuit may also enable the boost converter at 808, and setthe target bus voltage to V_(BUS-MAX) at 810.

If the control circuit determines that DC voltage is coupled to theinput terminals at 802, then the control circuit may operate in DC modeat 812. For example, the control circuit may ensure that the buscapacitor is disconnected at 814. For instance, the control circuit maydisconnect the bus capacitor by opening the switch (e.g., thecontrollable switching circuit 192) at 814. At 816, the control circuitmay determine whether the power P_(LOAD) required by the electrical loadexceeds a threshold amount P_(TH) (e.g., approximately 80%). If thecontrol circuit determines that the power P_(LOAD) required by theelectrical load does not exceed the threshold amount P_(TH) at 816, thenthe control circuit may disable the boost converter at 818. For example,the control circuit may disable the boost converter to reduce power lossin the LED driver, for example, due to the power loss in the boostconverter when enabled. When disabled, the boost converter may passthrough the DC voltage from the input terminals, and the bus voltageV_(BUS) may have a minimum magnitude V_(BUS-MIN) (e.g., approximately380 volts). In some instances, when operating in the DC mode, thecontrol circuit may be configured to enable the boost converter during astartup routine (not shown) of the LED driver, and disable the boostconverter during normal operation.

If the control circuit determines that the power P_(LOAD) required bythe electrical load does exceed the threshold amount P_(TH) at 816, thenthe control circuit may enable the boost converter at 820. At 822, thecontrol circuit may set the target bus voltage according to the powerrequired. For example, the control circuit may be configured to controlthe target bus voltage V_(BUS-TARGET) as a function of the powerP_(LOAD) required by LED light source 102. The control circuit may beconfigured to adjust the target bus voltage V_(BUS-TARGET) linearlybetween the minimum magnitude V_(BUS-MIN) and the maximum magnitudeV_(BUS-MAX) when the power P_(LOAD) required by LED light source isabove the threshold amount P_(TH). The control circuit may be configuredto control the target bus voltage V_(BUS-TARGET) using open loopcontrol, for example, by using a lookup table to determine the targetbus voltage V_(BUS-TARGET) in response to the target intensity L_(TRGT)and/or target load current I_(TRGT). The control circuit may beconfigured to control the target bus voltage V_(BUS-TARGET) using closedloop control, for example, by using the load voltage feedback signalV_(V-LOAD) and the load current feedback signal V_(I-LOAD) to determinethe power P_(LOAD) required by LED light source. The control circuit maybe configured to learn the target intensity L_(TRGT) and/or the targetload current I_(TRGT) at which the power P_(LOAD) required by LED lightsource exceeds the threshold amount P_(TH) (e.g., during a startuproutine).

Although described with reference to an LED driver, one or moreembodiments described herein may be used with other load controldevices. Also, a single control circuit may be coupled to, and/oradapted to, control multiple types of electrical loads in a load controlsystem.

What is claimed is:
 1. A load control device for controlling powerdelivered from a power source to an electrical load, the load controldevice configured to receive an input voltage from the power source, theload control device comprising: a power converter configured to generatea bus voltage; a load regulation circuit configured to receive the busvoltage and to control the power delivered to the electrical load; arectifier circuit configured to receive the input voltage from the powersource, the rectifier circuit configured to rectify the input voltage togenerate a rectified voltage and provide the rectified voltage to thepower converter when the input voltage is an AC voltage, the rectifiercircuit further configured to pass through the input voltage to thepower converter when the input voltage is a DC voltage, the rectifiercomprising first and second input terminals, first and second outputterminals, a first controllable switching circuit, and a secondcontrollable switching circuit, the first and second switching circuitsrendered non-conductive when the input voltage is an AC voltage andrendered conductive when the input voltage is a DC voltage; and acontrol circuit configured to control the load regulation circuit tocontrol the power delivered to the electrical load, the control circuitconfigured to operate in an AC mode when the input voltage is an ACvoltage and in a DC mode when the input voltage is a DC voltage; whereinthe control circuit is configured to disable the power converter whenoperating in the DC mode.
 2. The load control device of claim 1, whereinthe rectifier circuit comprises: a first diode configured to conductcurrent from the first input terminal to the first output terminal; asecond diode configured to conduct current from the second outputterminal to the second input terminal; a third diode configured toconduct current from the second input terminal to the first outputterminal; and a fourth diode configured to conduct current from thesecond output terminal to the first input terminal; wherein the firstcontrollable switching circuit is coupled in parallel with the firstdiode and the second controllable switching circuit is coupled inparallel with the second diode.
 3. The load control device of claim 2,wherein the first and second controllable switching circuits eachcomprise a MOSFET.
 4. The load control device of claim 3, wherein thefirst and second diodes are body diodes of the MOSFETs of the first andsecond controllable switching circuits.
 5. The load control device ofclaim 1, wherein the rectifier circuit comprises a DC detect circuitelectrically coupled between input terminals of the rectifier circuit,the DC detect circuit configured to render first and second controllableswitching circuits of the rectifier circuit conductive when the voltageacross the DC detect circuit is a DC voltage.
 6. The load control deviceof claim 1, wherein the control circuit is configured to disable thepower converter when the power required by the load is less than athreshold amount in the DC mode.
 7. The load control device of claim 6,wherein the control circuit is configured to control the power converterto adjust the magnitude of the bus voltage towards a target bus voltage,the control circuit configured to adjust the target bus voltage as afunction of the power required by the electrical load when the powerrequired by the electrical load is greater than the threshold amount inthe DC mode.
 8. The load control device of claim 1, further comprising:a ripple detect circuit configured to receive a rectified voltage andgenerate a ripple detect signal that indicates whether AC ripple ispresent in the rectified voltage; wherein the control circuit isconfigured to receive the ripple detect signal, and determine whetherthe input voltage is AC voltage or DC voltage based on the ripple detectsignal.
 9. The load control device of claim 1, wherein the controlcircuit is configured to enable the power converter during a startuproutine of the load control device when operating in the DC mode, andconfigured to disable the power converter during normal operation whenoperating in the DC mode.
 10. The load control device of claim 1,further comprising: a bus capacitor; and a controllable switchingcircuit electrically coupled in series with the bus capacitor, thecontrol circuit configured to render the controllable switching circuitnon-conductive when operating in the DC mode to disconnect the buscapacitor.
 11. The load control device of claim 1, wherein the controlcircuit is configured to generate a bus voltage control signal andprovide the bus voltage control signal to the power converter; andwherein the power converter is configured to adjust a magnitude of thebus voltage towards a target bus voltage based on the bus voltagecontrol signal.
 12. The load control device of claim 1, wherein thepower converter is configured to generate a bus voltage feedback controlsignal that indicates a magnitude of the bus voltage, and provide thebus voltage feedback control signal to the control circuit.
 13. The loadcontrol device of claim 1, wherein the control circuit is configured todisable the power converter by allowing the DC voltage to pass throughthe power converter so that the bus voltage has a minimum bus voltagemagnitude.
 14. A load control device for controlling power deliveredfrom a power source to an electrical load, the load control deviceconfigured to receive an input voltage from the power source, the loadcontrol device comprising: a power converter configured to receive theinput voltage or a rectified version of the input voltage and generate abus voltage; a load regulation circuit configured to receive the busvoltage and to control the power delivered to the electrical load; and acontrol circuit configured to control the load regulation circuit tocontrol the power delivered to the electrical load, the control circuitis configured to control the power converter to adjust the magnitude ofthe bus voltage towards a target bus voltage, the control circuitconfigured to operate in an AC mode when the input voltage is an ACvoltage and in a DC mode when the input voltage is a DC voltage; whereinthe control circuit is configured to decrease the target bus voltagewhen operating in the DC mode.
 15. The load control device of claim 14,wherein the control circuit is configured to control the power converterto adjust a magnitude of the bus voltage towards a target bus voltage,the control circuit configured to adjust the target bus voltage as afunction of the power required by the electrical load when the powerrequired by the electrical load is greater than a threshold amount inthe DC mode.
 16. The load control device of claim 14, furthercomprising: a rectifier circuit configured to receive the input voltagefrom the power source, the rectifier circuit configured to rectify theinput voltage to generate the rectified version of the input voltagewhen the input voltage is the AC voltage, and the rectifier circuitconfigured to pass through the input voltage when the input voltage isthe DC voltage.
 17. The load control device of claim 16, wherein therectifier circuit comprises a DC detect circuit electrically coupledbetween input terminals of the rectifier circuit, the DC detect circuitconfigured to render first and second controllable switching circuits ofthe rectifier circuit conductive when the voltage across the DC detectcircuit is a DC voltage.
 18. The load control device of claim 14,further comprising: a ripple detect circuit configured to receive arectified voltage and generate a ripple detect signal that indicateswhether AC ripple is present in the rectified voltage; wherein thecontrol circuit is configured to receive the ripple detect signal, anddetermine whether the input voltage is AC voltage or DC voltage based onthe ripple detect signal.
 19. A load control device for controllingpower delivered from a power source to an electrical load, the loadcontrol device configured to receive an input voltage from the powersource, the load control device comprising: a power converter configuredto receive the input voltage or a rectified version of the input voltageand generate a bus voltage across a bus capacitor; a load regulationcircuit configured to receive the bus voltage and to control the powerdelivered to the electrical load; a controllable switching circuitelectrically coupled in series with the bus capacitor; and a controlcircuit configured to control the load regulation circuit to control thepower delivered to the electrical load, the control circuit configuredto operate in an AC mode when the input voltage is an AC voltage and ina DC mode when the input voltage is a DC voltage; wherein the controlcircuit is configured to render the controllable switching circuitconductive in the AC mode and non-conductive in the DC mode.